The present invention relates to an apparatus for producing a polishing solution and an apparatus for feeding the polishing solution, and more particularly, to an apparatus for producing a chemical-mechanical polishing solution for use in polishing in a semiconductor device-manufacturing process and an apparatus for feeding such a polishing solution which are capable of controlling the generation of abrasive grains having a particle size larger than a predetermined value in the polishing solution in an in-line and continuous manner.
Semiconductor devices have been required to be highly integrated and operated at a higher speed and with a lower consumption of electric power. In the semiconductor manufacturing process, for the purpose of flattening the surface of metallic wiring or layer insulation film formed on a semiconductor wafer during an intermediate step, the surface of the semiconductor wafer is subjected to chemical-mechanical polishing using, for example, a silica-based polishing solution (CMP slurry). In recent years, in view of mass-production of the semiconductor devices and difficulty in controlling the composition of the polishing solution, the polishing solution has been produced during the polishing step. Upon the production of the polishing solution, in order to achieve an accurate polishing rate, the concentration of abrasive grains in the polishing solution must be strictly controlled. Further, the abrasive grains contained in the polishing solution tend to be gradually agglomerated together, and the thus agglomerated abrasive grains in the form of large grains tend to cause undesirable scratches on the surface of the semiconductor wafer. Therefore, it becomes more important to monitor and control the size of the abrasive grains contained in the polishing solution.
Upon the production of the polishing solution, the polishing solution as produced is sampled and diluted with pure water. The diluted polishing solution is then irradiated with a predetermined quantity of light to measure an intensity of transmitted light or scattered light, followed by determining the number of large abrasive grains contained in the polishing solution from the measured light intensity. The reason why such a sampling method must be used for controlling the polishing solution is as follows. That is, if the polishing solution is directly measured on the production line, the number of abrasive grains contained in it cannot be accurately measured. This is because the flow rate of the solution tends to be fluctuated by pulsation flow of the solution due to a pump or the like. Also, in the case of the above silica-based polishing solution, the solution contains adequate silica particles having an average particle size of about 0.2 xcexcm at a concentration as high as 1013/ml and has a lesser content of large abrasive grains to be controlled. Therefore, for example, in the case where the agglomerated large abrasive grains of not less than 3 xcexcm are detected by directly measuring the attenuation of irradiated light due to the existence of the large abrasive grains, it is difficult to measure such a light attenuation due to the large abrasive grains since considerable light attenuation is caused by the existence of a large amount of the adequate abrasive grains.
Meanwhile, since the detection of the large abrasive grains contained in the polishing solution requires a relatively long time, the polishing solution actually used will be changed in particle size distribution from the initially sampled one. More specifically, the polishing solution used contains a larger amount of agglomerated abrasive grains than that upon sampling since the agglomeration of the abrasive grains proceeds further. As a result, in the polishing step, there is a possibility that the semiconductor wafer suffers from considerable scratches beyond expectation.
An object of the present invention is to provide an apparatus for producing a chemical-mechanical polishing solution for use in a polishing step of a semiconductor device-manufacturing process which is capable of controlling the generation of large (coarse) abrasive grains having a particle size larger than a predetermined (fixed or designed) value in the polishing solution in an in-line and continuous manner with a high accuracy.
Another object of the present invention is to provide an apparatus for feeding a chemical-mechanical polishing solution for use in a polishing step of a semiconductor device-manufacturing process which is capable of controlling the generation of large (coarse) abrasive grains having a particle size larger than a predetermined (fixed or designed) value in the polishing solution in an in-line and continuous manner with a still higher accuracy.
To accomplish the aims, in a first aspect of the present invention, there is provided an apparatus for producing a polishing solution mainly comprising pure water and abrasive grains, which apparatus comprises:
a preparation tank (2) for preparing a polishing solution containing abrasive grains at a predetermined concentration, by mixing a abrasive grain-containing slurry as a feedstock and pure water with each other; and
a circulation device (L4) for circulating the thus prepared polishing solution so as to keep the solution in a suspended state.
The circulation device (L4) includes a circulation conduit (56) for circulating the polishing solution, and a flow-controllable bypass conduit (561) fluidly associated with the circulation conduit (56) and is provided with a particle detector (7) for monitoring the polishing solution so as to detect large abrasive grains not smaller than a predetermined value and measure the number of the large abrasive grains.
The particle detector (7) is of the light-extinction type and is adapted for irradiating a predetermined quantity of light on a flow cell (74) fitted in the bypass conduit (561) so as to detect an attenuation of the light transmitted through the polishing solution flowing through the flow cell (74) due to the large abrasive grains.
The flow cell (74) allows the polishing solution to flow through it at a constant flow rate by flow control of the bypass conduit (561).
In a second aspect of the present invention, there is provided a production apparatus according to the above first aspect, also including a polishing solution feed device (L5) connected to a downstream side of the circulation device (L4) for feeding the polishing solution circulated through the circulation device (L4) to a polishing apparatus (9).
The polishing solution feed device (L5) includes a feed conduit (57) for feeding the polishing solution, and a flow-controllable bypass conduit (571) fluidly associated with the feed conduit (57). The flow-controllable bypass conduit (571) is provided with a particle detector (8) for monitoring the polishing solution so as to detect large abrasive grains not smaller than a predetermined value and measure the number of the large abrasive grains.
The particle detector (8) is of the light-extinction type and is adapted for irradiating a predetermined quantity of light on a flow cell fitted in the bypass conduit (571) so as to detect an attenuation of the light transmitted through the polishing solution flowing through the flow cell due to the large abrasive grains.
The flow cell allows the polishing solution to flow through it at a constant flow rate by flow control of the bypass conduit (571).
In a third aspect of the present invention, there is provided an apparatus for feeding a polishing solution mainly comprising pure water and abrasive grains to a polishing apparatus (9), which includes a feed conduit (57) extending from a polishing solution feed source (S1) to the polishing apparatus (9), and a flow-controllable bypass conduit (571) fluidly associated with the feed conduit (57), the flow-controllable bypass conduit (571) being provided with a particle detector (8) for monitoring the polishing solution so as to detect large abrasive grains not smaller than a predetermined value and measure the number of the large abrasive grains.
The particle detector (8) is of the light-extinction type and is adapted for irradiating a predetermined quantity of light on a flow cell (84) fitted in the bypass conduit (57) so as to detect an attenuation of the light transmitted through the polishing solution flowing through the flow cell (84) due to the large abrasive grains.
The flow cell (84) allows the polishing solution to flow through it at a constant flow rate by flow control of the bypass conduit (571).